Kotlin List first()
Syntax & Examples

Syntax of List.first()

There are 2 variations for the syntax of List.first() extension function. They are:

fun <T> List<T>.first(): T

This extension function returns the first element.

fun <T> Iterable<T>.first(predicate: (T) -> Boolean): T

This extension function returns the first element matching the given predicate.

✐ Examples

1 Example

In this example,

We create a list named list1 containing integers.
We use the first() function on list1 to get the first element.
The first element of list1 is stored in result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list1 = listOf(1, 2, 3, 4, 5)
    val result = list1.first()
    println(result)
}

Output

2 Example

In this example,

We create a list named list2 containing strings.
We use the first function on list2 with a predicate that finds the first string with length greater than 5.
The first string with length greater than 5 in list2 is stored in result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list2 = listOf("apple", "banana", "cherry")
    val result = list2.first { it.length > 5 }
    println(result)
}

Output

banana

3 Example

In this example,

We create a list named list3 containing characters.
We use the first function on list3 with a predicate that finds the first lowercase character.
The first lowercase character in list3 is stored in result.
Finally, we print the value of result to standard output using the println statement.

Kotlin Program

fun main(args: Array<String>) {
    val list3 = listOf('a', 'b', 'c', 'd', 'e')
    val result = list3.first { it.isLowerCase() }
    println(result)
}

Output

Summary

In this Kotlin tutorial, we learned about first() extension function of List: the syntax and few working examples with output and detailed explanation for each example.